Conventionally, in general, a throttle valve for controlling a flow rate of air sucked into an internal combustion engine is interconnected to an acceleration pedal through a wire so that a driver controls the opening and closing of the throttle valve by operating the acceleration pedal. In contrast, in recent years, an electronic control throttle device has been spread in which positions of an acceleration pedal and a throttle valve as well as an operating state are detected, then a target position of the throttle valve is obtained by a microcomputer, and the throttle valve is controlled by a motor so as to trace the target position. The entirety of an air intake system can be simplified and reduced in cost by combining the electronic control throttle device with an idle control valve and an automatic cruise control device. In a direct fuel injection engine aiming the reduction of a fuel cost, since a relation between an engine torque desired by a driver indicated by an acceleration pedal position and an amount of air required for the desired engine torque changes largely depending on an operation state, it is difficult to mechanically link the acceleration pedal with a throttle valve.
Since the position control of the electronic control throttle device is performed so that the position of the throttle valve coincides with a target position, the reliability of a throttle position sensor is very important. In general, a potentiometer attached to the rotation shaft of the throttle valve is used in order to measure the position of the throttle valve. The potentiometer is a sensor which is arranged in a manner that a brush fixed to the rotation shaft contacts with a resistor disposed concentrically along the rotation direction of the shaft to divide a voltage at the contact point, whereby the divided voltage indicates the contact position. Another device for detecting the position of a throttle valve is also known in which a non-contact type sensor using hall-effect is provided at the throttle valve position detection unit in place of the potentiometer in order to improve the durability of the detection unit.